Thread cutting mechanism for lockstitch sewing machines



March 16, 1965 H. ADAM 3,173,393

THREAD CUTTING MECHANISM FOR LOCKSTITCH SEWING MACHINES Filed Dec. 12,1962 2 Sheets-Sheet 1 By W m ATTOE/VE Y H. ADAM March 16, 1965 THREADCUTTING MECHANISM FOR LOCKSTITCH SEWING MACHINES Filed Dec. 12, 1962 2Sheets-Sheet 2 United States Patent Claims. (a. 112-452 The presentinvention relates to thread cutting and control mechanism for sewingmachines, more particularly to machines of the type including a rotarylooper or loop taker cooperating with a reciprocating needle for theproduction of lockstitches, in a manner well known in the art.

An important object of the invention is the provision of improved threadtrimming mechanism for machines of the above type by means of which boththe upper or needle thread and the lower or looper thread may be cut inthe proper position at the end of a sewing operation by the provision ofa suitable catch-thread and trimming device operable during and incooperation with a normal needle operating or reciprocating cycle.

Another object of the invention is the provision of combined upper andlower thread trimming means of the type referred to, being operablyassociated with upper or needle thread locking means, whereby to enablea trimming of the needle thread with a minimum projecting length fromthe eye of the needle, while at the same time ensuring a safe andreliable initiation of the upper and lower thread interlock at thestarting of a subsequent seam or stitching operation.

Yet another object of the invention is the provision of unitary controlmeans in conjunction with upper and lower thread trimming and lockingmeans of a lockstitch sewing machine of the type referred to, toautomatically sew a predetermined number of initial or starting stitchesduring locking of the cut end of the needle thread.

There has already become known as described by US. patent applicationSerial No. 215,317, filed by Kristen Hedegaard, entitled Thread TrimmingMechanism for Lockstitch Sewing Machines, and assigned to the sameassignee as the instant application thread trimming mechanism or devicesfor lockstitch sewing machines including a rotary loop taker andutilizing a catch-thread and trimming device cooperating with astationary cutter at a predetermined loop taker position or position ofthe upper and lower threads during the loopforming period of a completeneedle oscillating cycle or operation. More particularly, in the knownarrangement the catch-thread and trimming device is operated in a to andfro or oscillating movement upon reaching the predetermined loop takerposition during a needle operating cycle, whereby to first trap the looptaker thread and the work limb of the needle thread loop during onehalf-cycle movement'of said device, and to subsequently out both threadsby the stationary cutting knife during the remaining half-cycle ormovement of the device in the opposite direction.

In thread trimming devices of the aforementioned and other types, it isnecessary, in order to prevent unthreading or disengagement of theneedle thread from the needle during the first stitch formationsubsequent to a thread trimming operation, to sever the needle thread ata point sufficiently spaced from the needle, that is, to ensure anadequate projecting length of the cut thread from the eye of the needle,in an eliort to enable a safe and reliable thread interlock between theupper and lower threads at the commencement of a new stitchingoperation. This has the disadvantage, among others, that the beginningof the needle thread may not be fully drawn through the 3,173,393Patented Mar. 16, 1965 work or fabric during the subsequent stitchingcycle and as a result will project from the top or upper surface of thework or fabric. This condition is highly objectionable In many cases, inparticular in ornamental stitching, so that it becomes necessary tosubsequently remove or cut the undesirable projecting thread ends, or tomanually draw the same through and to the underside of the work.

Aside from ornamental stitching and the like special sewing operations,it is generally desirable, if not imperative, to cut the needle threadat a point as close as possible to the needle without endangering thesafe and reliable thread interlock during the initial stitches of asubsequent sewing operation.

A more specific object of the present invention is, therefore, theprovision of means in conjunction with an upper and lower threadtrimming device of the general type referred to, wherein the drive oroperating means of said device, being synchronized with the needleoperation, is additionally utilized to temporarily operate a suitableupper thread clamping or locking device, to ensure a safe initiation ofa new lockstitch operation subsequently to a thread cutting operation.

The invention, both as to the foregoing and ancillary objects and novelaspects thereof, will be better understood from the following detaileddescription of a preferred practical embodiment, taken in conjunctionwith the accompanying drawings forming part of this specification and inwhich:

FIG. 1 is a general elevational view of a sewing machine, shown partlyin section, and embodying threadtrimming and locking means constructedin accordance with the principles of the invention;

FIG. 2 is a partial perspective view showing the catchthread andtrimming device and the unitary control cam therefor being embodied inthe machine according to FIG. 1;

FIG. 3 is a front view of the thread-trimming and locking device withthe stitching plate of the machine being shown in section;

FIG. 4 is a plan view partly shown in section of the coupling mechanismfor the thread-trimming and locking device;

FIG. 5 is a partial plan view of the thread-trimming and locking device;

FIG. 6 is a sectional view taken on line VIVI of FIG. 4;

FIG. 7 is a sectional view taken on line VIIVII of FIG. 3; and

FIG. 8 is an electrical circuit diagram schematically illustrating theoperation of the thread cutter, locking device and starting switchcontrol in accordance with the invention.

Like reference numerals denote like parts and elements in the differentviews of the drawings.

With the foregoing objects in view, the invention, according to one ofits aspects, involves generally the provision of a conventionallockstitch sewing machine of the type including a throat or stitchingplate, a reciprocating needle above said plate and a rotary loop takerhaving a needle thread seizing beak and mounted below said plate forcooperation with said needle, to produce lockstitches by the needle andlooper threads, with thread trimming mechanism comprising a catchthreaddevice disposed close to the outer surface of said loop taker forrotation coaxially therewith, said device, in the preferred embodiment,having a recess and adjoining triangular projection pointing in adirection opposite to said beak, whereby to catch and trap both thelooper thread and the work limb of the needle thread loop formed by saidloop taker upon rotation of said device from a predetermined startingposition in respect to and synchronously with a needle oscillating oroperating cycle, said projection preferably moving in a directionopposite to said beak. Said device is furthermore provided with firstcutting means in the form of a cutting knife for cooperation with astationary plate or cutter, to sever both said threads in the trappedposition during an active needle oscillating or operating cycle of themachine.

There is furthermore provided in accordance with the present inventionsuitable means to couple said catchthread device with the driving shaftof the machine at a predetermined position during the needle operatingcycle, to initiate the thread cutting operation and to arrest the devicefor subsequent use.

Furthermore, according to another aspect of the present invention, thereis provided means being operably associated with the thread trimmingmechanism to continue the loop taker and needle operation during alimited number of needle operating cycles subsequently to the threadtrimming operation and before arresting the device, for the actuation ofa needle thread clamping or locking device during a predetermined numberof initial or starting stitches of a subsequent sewing operation withthe cut end of the upper thread in the locked position, to ensure a safeand reliable starting or interlock of the upper and lower threads duringcommencement of said sewing operation. As a result, the threads, inparticular the needle thread may be cut at a point being at a minimumdistance from the eye of the needle, to prevent the end of the threadfrom projecting from the work, as well as to avoid other defects and togenerally improve and stabilize the thread interlock or stitch formationat the start of a new seam or sewing pattern.

For the foregoing purpose, the catch-thread and trimming device rotatingtogether with the loop taker is advantageously fitted with a control camcooperating with suitable cam follower means which, in turn, serves tocontrol a needle thread clamping slide or the like, said cam having acontrol surface or contour such as to effect, during a completerevolution thereof corresponding to a predetermined number of loop takerrevolutions or needle oscillating cycles, the integrated sequentialoperations of catching and cutting the threads, of locking the needlethread, performing a desired number of subsequent initial or startingstitches with the needle thread in the locked condition, and finallyunlocking the thread for the continuance of ordinary stitching by themachine.

In order to initiate the thread trimming operation, the locking andinitial stitch formation, the catch-thread device and control cam may becoupled with the drive shaft of the machine through a suitablereleasable coupling device preferably operated by means of a solenoid inconjunction with suitable further means to initiate the couplingconnection at a predetermined position during the needle oscillatingcycle, that is, during the downward needle movement, while disconnectionof the device may be effected upon a complete revolution of the cam byde-energization of said solenoid, in a manner as will become furtherapparent as the following description proceeds in reference to thedrawings.

Referring more particularly to FIG. 1, there is shown a conventionalsewing machine comprising a base 1 supporting an upright 2 from whichextends an overhanging upper arm 3 terminating in a sewing head 4.Mounted within the arm 3 is the main drive shaft 5 of the machine beingoperably connected with the vertically reciproeating needle bar 7carrying an eye-pointed needle 6 through which is passed in a knownmanner the upper or needle thread, FIGS. 2 and 3. Secured to the maindrive shaft 5 is a first pulley 8 which serves to impart rotation to anauxiliary shaft 11 parallel to shaft 5 and mounted in the base 1 by wayof a belt 9 and cooperating second pulley 10 mounted upon said auxiliaryshaft. Operably connected with the shaft 11, through a pair of gears 12,13 is the loop taker drive shaft 17 being supported by a pair of sleevesor bearings 14, 15 mounted within the lower or work supporting arm 16 ofthe sewing machine. The front end of shaft 17 carries a cylindricalrotary looper or loop taker 18 of known construction for cooperationwith the reciprocating needle 6 for the formation of lockstitches byinterlocking of the looper and needle threads in the ordinary manner.For this purpose, the looper 18 may have a needle thread seizing beak18' serving to draw out and cast off the needle thread loop formedduring rotation of the looper which, by a suitable design of thetransmission ratio 12, 13, may perform two revolutions during eachcomplete reciprocating oscillating cycle of the needle, as is customarywith conventional double lockstitch sewing machines.

The end of the auxiliary shaft 11 carries a further gear 19 which mesheswith a counter gear 20 being loosely mounted upon a hollow shaft 21,FIG. 4, between a flange 22 of said shaft and a sleeve or bushing 24secured in a supporting wall 23 attached to the lower arm 16 of thesewing machine. The hollow shaft 21 being driven, in the example shown,at a speed reduction 2:1 from the shaft 11 is, in turn, fixedlyconnected to a horizontal drive shaft 25 of the thread cutting andlocking device, said last-mentioned shaft being supported by a pair ofsleeves or bearings 26, 27, FIG. 1, and secured against axialdisplacement by the provision of a pair of setting or locking rings 28,29. Mounted at the lefthand end of shaft 25 is a pair of furthertransmission gears 30, 31 which together with the gears 19, 20 form atransmission system 32 producing a total speed reduction of 4:1 betweenthe shaft 11 and the driving gear 31 of the thread cutting and lockingdevice, in the case of the example illustrated. Gear 31 rotating at halfthe speed of gear 30 forms an integral unit with the catch-thread device33, FIG. 2, and is rotatably mounted upon the supporting or bearingsleeve 15 of the loop taker shaft 17 and secured against displacement bymeans of a locking ring 34. The catch-thread and trimming device 33 ofspecial construction has a recess 36 and adjoining triangular projection35, FIGS. 2 and 5, said recess pointing in a direction opposite to thebeak 18' and merging at the points 36 and 37 into a cross-piece orslightly arcuate plate 38 to the longitudinal edge of which is secured acutting knife or blade 39 adapted to cooperate with a stationary cuttingplate 40 mounted upon the underside of the throat or stitching plate 50'of the sewing machine forming part of the lower arm 16.

Secured to the catch-thread device 33 intermediate the cross-plate 38and the driving gear 31 and rotatable with the latter is a cam disk 41having profiled cam sections 41.1, 41.2, 41.3, 41.4, and 41.5, FIG. 3,in the example illustrated. Cam 41 is resiliently engaged by a camfollower roller 42, FIG. 3, through the action of a spring 43. Roller 42is mounted upon a lever 44 having one secured to a shaft 45 which isrotatably supported by the arm 16, the opposite end of said lever beingprovided with a slot to compensate for the radial movement thereof. Thethread clamping slide 47, being operably connected with the lever 44through a pin moving within the slot 46, is mounted upon the undersideof the stitching plate 50' by means of screws 4-9 movable within guideslots 48 of said plate which at its front end carries a wedge-shapedclamping element 51 having a triangular recess 52 for cooperation with astationary thread locking leaf spring 50.

The gear 20, FIGS. 4 and 6, being loosely mounted upon the hollow shaftor sleeve 21 has a lateral extension 53 being provided, in the case of atransmission ratio 2:1 between the gears 19, 2%), with two diametricallyopposed grooves or recesses 54. Furthermore, the flange 22 of the shaft21 is provided with two corresponding recesses or notches 55 adapted forengagement by a pair of coupling pins or fingers 56 axially extendingfrom the righthand side of a coupling sleeve 57 mounted upon and axiallydisplaceable relative to the shaft 25. The lefthand side of the couplingsleeve 57 has a nose or projection 58 being urged normally, that is, inthe de-coupled position of the coupling sleeve 57, to engage astationary recess 59 in the bearing 26 by the action of a tension spring65 to be described presently.

In order to displace the coupling sleeve 57, there is provided a lever60 having a pair of forked ends or arms 61, 62, FIG. 1, which carryrotatable rollers 63 engaging a central circular groove 64 of the sleeve57. Connected to the end of the arm 62 of the lever 611 is the tensionspring 65 which serves to urge the sleeve 57 to its inoperative orlocked position as shown in the drawing. Lever 60 is rotatably mountedby means of a pin 66 upon a split bolt 67 being, in turn, secured to thesupporting wall 68 of the arm 16 which also serves as a support for thebearing or sleeve 26. Lever 611 has a further arm 69 adapted to engagethe actuating rod 70 of an electromagnet or solenoid actuator 71 mountedupon the supporting wall 23 of the arm 16.

With specific reference to the example illustrated by the drawing, thegear ratios have been chosen to perform two initial or starting stitcheswith the cut needle thread and maintained in its locked position aftercutting of the threads. This has been found sufhcient to ensure a safeand reliable starting or stitch formation in commencing a new seam orsewing pattern. Inasmuch as a complete revolution of the shaft 11 oroscillating operating cycle of the needle is required for each of thecutting and thread locking operations, there follows a speed reductionratio of 4:1 between the shaft 11 and the driving gear 31 of the threadtrimming and locking device which ratio has been divided equally uponthe gear pairs 19, 20 and 3t), 31, respectively.

On the other hand, if a greater number such as, for example, fourinitial or starting stitches are desired, as in sewing relatively thinfabric pieces, a speed reduction of 6:1 by the gear ring 32 will berequired which may again be equally divided upon the gear pairs 19, 2t)and 3t 31. In such a case, that is, assuming that the gears 19, 20 havea transmission ratio of 3:1, the coupling sleeve 57 is provided withthree coupling pins or fingers 56 arranged at angular spacings of 120and cooperating with three similarly arranged grooves or recesses 54 and55 of the gear 20 and hollow shaft 21 respectively. In this manner,starting of the thread cutting and locking device 33 is ensured at theproper point within the needle operating or oscillating cycle, that is,during the downward movement of the needle within said cycle.

The operation of the thread cutting, locking and initial stitchformation afore-described is as follows:

After completion of a first sewing operation or upon reaching the end ofa seam, the solenoid 71 is energized during the downward movement of theneedle, for instance, by depressing a switch arm '75, FIG. 8, by meansof a pushbutton '76 or the like, to close a contact 77 in the solenoidoperating circuit. As a consequence, the actuating rod '70, FIG. 4,operates, by way of the lever 61B and rollers 63, the coupling sleeve5'7 from the rest position shown to its operative position with the twocoupling pins 56 of said sleeve passing through the grooves 55 of flange22 of shaft 21 and into the grooves 54 of the extension 53 of thecontinuously rotating driving gear 20. The latter is thus coupled withthe drive shaft 25 through the sleeve or hollow shaft 21. As aconsequence, the catch-thread device 33 is started to rotate in adirection opposite to the rotation of the looper 18 by way of the gearpair 30, 31, that is, both the device 33 and looper 18 rotate during thetime while the needle passes through the work or fabric and the beak 18'of the looper 18 draws the seized needle thread loop around the looperhousing, whereby the needle thread loop forms a triangle between thestitching plate 50' and the looper housing.

During continued rotation of the device 33, its point or projection 35penetrates the triangle of the needle thread, whereby to cause its limbadjoining the needle to engage the point 3'7 and to cause the looperthread and work limb of the needle thread to engage the projection 35.The looper thread and work limb of the needle thread loop are thusseparated from the needle thread limb of said loop and stretched, duringcontinued rotation of the device 33, between the stitching hole in theplate 51) and point 3%, across the cutting blade 41}, whereby to outboth said threads by cooperation of said blade with the cutting knife39.

The thread cutting operation takes place during a full revolution of themain drive shaft corresponding to a single needle operating cycle oroscillation or to a quarter revolution of the device 33 in the case ofthe example illustrated. During this partial rotation of the device 33,the follower roller 42 engages the concentric cam section 41.1 of thedisk 41, whereby the locking slide 47 remains in its rest or inoperativeposition.

The next following operating cycle, after the threads have been cut inthe manner described, again begins with a downward movement of theneedle, while the disk 41 continues to rotate in a direction opposite tothe looper 18. As a consequence, roller 42 engages the cam section 41.2of said disk, whereby to cause the locking slide 47 to be operatedtowards the right from its normal or rest position by the action of thespring 43. As a consequence, the slide assumes a position to the rightof the stitching hole in the plate 50' prior to the penetration of theneedle, the latter subsequently passing through the triangular recess 52while entering the work or fabric.

After the needle has again left the stitching plate 59' during itsfollowing upward movement, the roller 42 engages the cam section 41.3,thereby to return the slide 47 to the left against the action of spring43 and to cause the recess 52 to seize and lock the cut end of theneedle thread by the wedge 57 and spring 50, in the manner shown in FIG.3 of the drawings. As a result, the disk 41 has been rotated by afurther quarter revolution, to now cause the roller 42 to engage theconcentric cam section 41.4 of said disk.

During the subsequent formation of an initial or starting stitch, thedisk 41 performs a further quarter revolution with the roller 42 stillengaging the cam section 41.4 and the slide 47 remaining in the lockedposition shown in the drawing. Shortly before the commencement of thelast or second starting stitch, the roller 42 V engages thercam section41.5 of the disk 41, whereby to slightly move the slide 47 towards theright and to release the needle thread. Thereafter, de-energization ofthe solenoid will return the device to its starting position. This maybe accomplished in the manner illustrated by PEG. 8 by locking theswitch arm 75 by the nose 78 of a spring-urged locking lever 79 andunlocking the same by a cam 51] having a projection 81 adapted to engagethe end of said lever, cam 80 being either identical with the disk 41 ordriven in synchronism therewith.

There is thus provided by the invention operating and control mechanismwhich, upon being set in motion at the completion of a seam, causes apredetermined number of consecutive needle operating cycles with theupper and lower threads being cut during the first cycle, the cut end ofthe needle thread being locked during the second cycle, and a number ofstarting stitches being effected during the remaining cycles, for thepurpose and with the novel effects and advantages as pointed out herein.Where the operating cycles follow each other consecutively in the mannerdescribed, the work will be advanced during the second or locking cycleby the feed dog of the sewing machine, whereby to automatically startthe new seam immediately following the preceding seam. This operationmay be desirable, for instance, in the production of ornamentalstitching or in connection with the like sewing operations. On the otherhand,

if a greater interval is desired between the locking of the thread andthe starting of a new seam the switch 75 may be released or unlockedafter the thread locking operation by the provision of an additionalprojection upon the cam 8t (not shown) being properly spaced from theprojection 81. After the work has then been moved to the new sewingposition, starting of the initial stitches and unlocking of the threadmay be effected by renewed depression of the button 76, with the threadbeing unlocked subsequently, in a manner readily understood from theforegoing.

In summing up the operation of the cutting and locking device, theneedle at the beginning of a thread cutting operation moves in thedownward direction or, more specifically, may have traversed, at theinstant of coupling of the device 33 with the shaft 11 by the fingers56, a path corresponding to about 60 of a revolution of said shaft.Inasmuch as the cutting operation requires exactly one revolution of theshaft 11 or in turn the main drive shaft 5, the needle will assume thesame initial position at the termination of the thread cutting cycle.While the needle continues its second operating cycle, the roller 42engages the cam section 41.2, thus moving the slide 47 to the right.After the needle has again passed the stitching plate during its ensuingupward movement, the roller 42 engages the cam section 41.4, thusdisplacing the slide to the left and locking the needle thread untilshortly before the completion of the second starting stitch, in themanner described. After the needle, during the continued revolution ofthe shafts and It, has reached its upper dead center position, theroller 42 engages the cam section 41.5, thereby opening the thread clampand leaving the remaining 60 of the fourth revolution of said shafts forthe clamp and the device to return to its starting position byinterruption of the circuit of the solenoid 71 and resultant decouplingof the gear and shaft 21 at the instant of the nose 58 engaging therecess 59.

In the foregoing the invention has been described with reference to aspecific illustrative device. It Will be evident, however, thatmodifications and variations, as well as the substitution of equivalentparts and elements for those shown and disclosed herein forillustration, may be made without departing from the broader scope andspirit of the invention as set forth in the appended claims. Thespecification and drawings are accordingly to be regarded in anillustrative rather than in a restrictive sense.

I claim:

1. In combination with a lockstitch sewing machine including a stitchingplate, a. reciprocating needle above said plate, and a rotatingcylindrical loop taker mounted below said plate and synchronized withsaid needle, to form lock stitches by the needle and loop taker threads;thread trimming mechanism comprising an arcuate blade element having afront edge forming triangular projection and provided with a recessadjoining said projection, said element being disposed close to theouter surface of, and rotatable coaxially with said loop taker,operating means to initiate rotation of said element from a startingposition in predetermined relation to and in synchronism with a needleoperating cycle of said machine, first cutting means upon said element,and second stationary cutting means arranged for cooperation with saidfirst cutting means, said projection, said recess and said cutting meansdesigned to sequentially effect, during rotation of said element in asingle direction from said starting position, stretching and separationof the loop taker thread and work limb thread of the needle loop fromthe needle limb of said loop by said projection, trapping of theseparated threads by said recess, and severing of the trapped threads bysaid cutting means.

2. In combination with a lockstitch sewing machine of the type includinga stitching plate, a reciprocating needle above said plate, and arotating cylindrical loop taker below said plate having a needle threadseizing beak and synchronized with said needle, to form lock stitches bythe needle and loop taker threads; thread trimming mechanism comprisingan arcuate blade element disposed close to the outer surface of androtatable coaxially with and in a direction opposite to the rotation ofsaid loop taker, the front edge of said element having a triangularprojection pointing in the direction opposite to said beak and providedwith a recess adjoining said projection, operating means to initiaterotation of said element in synchronism with said needle and startingfrom a position in predetermined relation to a needle operating cycle,first cutting means upon said element, and second stationary cuttingmeans arranged for cooperation with said first cutting means, saidprojection, said recess and said cutting means designed to sequentiallyeffect, during rotation of said element in a single direction from saidstarting position, stretching and separation of the loop taker threadand the work limb thread of the needle loop from the needle limb of saidloop by said projection, trapping of the separated threads by saidrecess and severing of the trapped threads by said cutting means.

3. In thread trimming mechanism as claimed in claim 2, a drive shaft forsaid needle, said operating means comprising a releasable couplinginterposed between said shaft and said element and including a pair ofrelatively axially displaceable coupling members fitted respectivelywith coupling pins and cooperating recesses positioned relativelyangularly such as to effect coupling of said members at saidpredetermined starting position of said element.

4. In thread trimming mechanism as claimed in claim 1 including furthermeans to stop said element in a predetermined relative position to theneedle operating cycle upon release of said operating means.

5. In combination with a lockstitch sewing machine of the type includinga stitching plate, a reciprocating needle above said plate, and arotating cylindrical loop tal ter mounted below said plate andsynchronized with said needle, to form lock stitches by the needle andloop taker threads; thread trimming mechanism comprising an arcuateblade element having a triangular projection and provided with a recessadjoining said projection, said element disposed close to the outersurface of and rotatable coaxially with said loop taker, first operatingmeans to initiate rotation of said element in the direction of saidprojection from a predetermined starting position In relation to and insynchronism with a needle operating cycle, first cutting means upon saidelement, second sta tionary cutting means arranged for cooperation withsaid first cutting means, said projection, said recess and said cuttingmeans designed to sequentially effect, during a first needle operatingcycle, stretching and separation of the loop taker thread and the worklimb thread of the needle loop from the needle limb of said loop by saidro ection, trapping of the separated threads by said recess, andsevering of the trapped threads by said cutting means, second operatingmeans to lock the cut end of the needle thread during a subsequentneedle operating cycle, and unitary control means for said first andsecond operating means synchronized with said needle, to sequent1allyout said threads, to lock the cut end of the needle thread, and toproduce a predetermined number of starting stitches in the locked needlethread position during a corresponding number of consecutive needleoperating cycles.

6. In thread trimming and locking mechanism as claimed in claim 5, adrive shaft for said needle, said control means comprising a camsupporting and driving said element, and releasable coupling means fortemporarily connecting said cam with said shaft during a predeterminednumber of revolutions thereof corresponding to an equivalent number ofneedle operating cycles, and cam follower means to actuate said secondoperating means, said cam being designed to actuate said secondoperating means during the needle operating cycle following theseparation of said threads during said first operating cycle.

7. In thread trimming and locking mechanism as claimed in claim 6, saidcoupling means including a pair of relatively axially displaceablecoupling members fitted respectively with projecting coupling pins andcooperating recesses positioned relatively angular-1y such as to effectcoupling of said members at a position corresponding to said startingposition of said element.

8. In combination with a sewing machine including a stitching plate, areciprocating needle above said plate, a drive shaft for said needle, arotating cylindrical loop taker having a needle thread seizing beak andmounted below said plate for cooperation with said needle, to producelock stitches; thread trimming mechanism comprising an arcuate bladeelement having a triangular projection and an adjoining recess anddisposed close to the outer surface of and rotatable coaxially with andin a direction opposite to said loop taker, operating means to initiaterotation of said element from a starting position in predeterminedrelation to and in synchronism with an operating cycle of said needle,to separate the loop taker thread and the work limb of the needle threadloop from the needle limb of said loop by said projection and to trapthe separate threads by said recess, first cutting means upon saidelement, and cooperating stationary cutting means, to sever the trappedthreads during a first needle operating cycle, locking mechanism to lockthe cut end of the needle thread during a subsequent needle operatingcycle, and unitary control means synchronized with said needle, tosequentially operate said thread trimming and locking mechanisms and toproduce a predetermined number of starting stitches in the locked 10needle thread position during a corresponding number of consecutiveneedle operating cycles, and means to unlock said needle thread by saidcontrol means upon termination of said starting stitches.

9. In thread trimming and locking mechanism as claimed in claim 8, saidcontrol means comprising a cam supporting and driving said element andreleasable cou pling means to temporarily connect said cam With saiddrive shaft during a predetermined number of revolutions thereof, and acam follower to actuate said locking mechanisms, said cam being designedto effect operation of said locking mechanism during the needleoperating cycle following said first operating cycle.

10. In thread trimming and locking mechanism as claimed in claim 8, saidcoupling means including a pair of relatively axially displaceablecoupling members fitted respectively with projecting coupling pins andcooperating recesses positioned relatively angularly such as to effectcoupling of said members at a relative position corresponding to thestarting position of said element.

References Cited by the Examiner UNITED STATES PATENTS 343,992 6/86Heberling 112253 757,463 4/04 Hogan 112253 X 768,111 8/04 Burghardt112252 904,463 11/08 Taylor 19240 X 1,401,973 1/22 Fifield 1122521,883,654 10/32 Ericsson 112-252 2,376,417 5/45 Chudner 1l2-2522,858,786 11/58 Benink 112-252 JORDAN FRANKLIN, Primary Examiner. DAVIDJ. WILLIAMOWSKY, Examiner.

1. IN COMBINATION WITH A LOCKSTITCH SEWING MACHINE INCLUDING A STITCHINGPLATE, A RECIPROCATING NEEDLE ABOVE SAID PLATE, AND A ROTATINGCYLINDRICAL LOOP TAKER MOUNTED BELOW SAID PLATE AND SYNCHRONIZED WITHSAID NEEDLE, TO FORM LOCK STITCHES BY THE NEEDLE AND LOOP TAKER THREADS;THREAD TRIMMING MECHANISM COMPRISING AN ARCUATE BLADE ELEMENT HAVING AFRONT EDGE FORMING TRIANGULAR PROJECTION AND PROVIDED WITH A RECESSADJOINING SAID PROJECTION, SAID ELEMENT BEING DISPOSED CLOSE TO THEOUTER SURFACE OF, AND ROTATABLE COAXIALLY WITH SAID LOOP TAKER,OPERATING MEANS TO INITIATE ROTATION OF SAID ELEMENT FROM A STARTINGPOSITION IN PREDETERMINED RELATION TO AND IN SYNCHRONISM